(i) Technical Field
The present invention relates to a semiconductor device.
(ii) Related Art
A HEMT (High Electron Mobility Transistor) using nitride semiconductor is being used as an output amplifier element for a high frequency wave. The HEMT uses a two-dimensional electron gas (2DEG) generated at an interface between a channel layer and an electron supply layer as a carrier. There is a HEMT using a semiconductor substrate. When a trap in the substrate captures an electron in the 2DEG, a current may be reduced. And a leak current may occur because of the conductivity of the substrate. There is a case where a buffer layer is provided in order to restrain the current reduction and the leak current. Japanese Patent Application Publication No. 2010-232377 discloses an invention in which a composition ratio of aluminum (Al) in the buffer layer is adjusted.